Conventionally, to limit undesirable temperature buildup in the photocells, the radiation spectrum from the heated object is filtered to illuminate the photocells only with photons of near optimal energy corresponding to the band gap of the semiconductor used to fabricate the cells. In order to effectively utilize the available radiation from the heated object, the semiconductor used in the photocells must have a band gap which energetically corresponds to that of the peak of the radiation spectrum emitted by the source. TPV generators of the prior art have typically employed costly unconventional small band gap semiconductors, such as GaSb, in photocells designed to match the radiation spectral peak of objects heated to the order of 1400 degrees Kelvin. Much higher temperatures on the order of 2200.degree. K., are required to heat objects sufficiently to produce a spectrum suitable to illuminate conventional silicon cells in a TPV generator. Such high temperatures introduce many complications and the use of cheap silicon cells has been therefore prohibitive.